Hydraulic machines such as dozers, loaders, excavators, backhoes, motor graders, and other types of heavy equipment use one or more hydraulic actuators to accomplish a variety of tasks. These actuators are fluidly connected to a pump of the machine that provides pressurized fluid to chambers within the actuators, and also connected to a sump of the machine that receives low-pressure fluid discharged from the chambers of the actuators. As the fluid moves through the chambers, the pressure of the fluid acts on hydraulic surfaces of the chambers to affect movement of the actuators. A flow rate of fluid through the actuators corresponds to a velocity of the actuators, while a pressure differential across the actuators corresponds to a force of the actuators.
Control over the speed and/or force of hydraulic actuators can be provided by way of one or more metering valves. For example, a first metering valve controls fluid flow into a head-end of a hydraulic cylinder, while a second metering valve controls fluid flow out of the head-end. Likewise, a third metering valve controls fluid flow into a rod-end of the hydraulic cylinder, while a fourth metering valve controls fluid flow out of the rod-end. The different metering valves are cooperatively opened and closed (e.g., based on operator input) to cause fluid to flow into one end of the hydraulic cylinder and simultaneously out of an opposing end, thereby extending or retracting the hydraulic cylinder.
An exemplary metering valve is disclosed in U.S. Patent Publication No. 2014/0034135 of Beschorner et al. that published on Feb. 6, 2014 (“the '135 publication”). In particular, the '135 publication discloses a valve having a body, and a valve element slidingly disposed within the body. The valve element includes a first land, a second land axially spaced from the first land, and a check stem disposed about a portion of the first land. The check stem is enlarged and extends radially beyond the first land to selectively engage an inner surface of the body. A sleeve is disposed about a portion of the second land and is fixedly engaged to the inner surface of the body. A seal is disposed about the second land, between the second land and the sleeve. The seal and the second land separate a working chamber from a control chamber and move together axially within the sleeve.
Although the valve of the '135 publication may be suitable for many applications, the valve may be less than optimal for other applications. In particular, the sleeve may be used only to fill a space within the body that allows assembly of the enlarged check stem into the body. The sleeve may add cost and weight to the valve.
The disclosed valve and spool are directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.